Optimal nitrogen rates and clonal effects on cannabinoid yields of medicinal cannabis

Nitrogen (N) nutrition and germplasm of clones can influence biomass and cannabinoid concentration in medicinal cannabis. However, there are discrepancies on the optimal nitrogen (N) application rate at the flowering stage to achieve maximum yield and if, or how, this interacts with clones from different seed lines of the same genotype. This research examined the relationship between N application rate, concentration of cannabinoids and biomass yield of a CBD-type medicinal cannabis cultivar in clones propagated from five different seed lines (hereafter referred to as clones). Clonal rooted cuttings were propagated from five mother plants germinated from seeds of cultivar 'Tas1'. Five N levels (30, 90, 160, 240 and 400 mg/L N) were imposed at the start of the inflorescence period and continued until harvest eight weeks later. Some pollen contamination occurred during the trial so that seed biomass was assessed for each plant and included in statistical analysis. Weight of total biomass, leaves and inflorescence (from upper and lower canopy positions), N%, and cannabinoid concentrations were measured after the harvest. Results indicated that increasing N supply generated a clear upward trend in inflorescence biomass that peaked at 160 mg/L N after which it did not significantly change, while leaf biomass steadily increased with N. Delta9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations decreased significantly with increasing N concentration in leaves with a similar, but non-significant, trend for inflorescences. The CBD to THC ratio increased with increased N. Clone source was strongly correlated with cannabinoid concentration, but not leaf, inflorescence or total biomass, across all N treatments. Clones 13 and 27 developed greater cannabinoid concentrations relative to clones 18 and 26 irrespective of N treatment. Pollen contamination induced seed development that comprised up to 5% of inflorescence biomass dry weight but this did not significantly affect whole-plant biomass, N accumulation (N%), or cannabinoid concentration. These findings provide valuable insights for improving cannabinoid yield in this widely cultivated plant species.